Spur estimating receiver system

ABSTRACT

One example includes a receiver system. The receiver system includes an analog-to-digital converter (ADC) configured to convert an analog input signal into a digital output signal at a sampling frequency. The receiver system also includes a spur correction system configured to receive the digital output signal and to estimate spurs associated with the digital output signal and to selectively correct a subset of the spurs associated with a set of frequencies that are based on the sampling frequency.

RELATED APPLICATIONS

This application claims priority from India Provisional ApplicationSerial No. 201941040005, filed 3 Oct. 2019, which is incorporated hereinin its entirety.

TECHNICAL FIELD

This disclosure relates generally to electronic systems, and morespecifically to a spur estimating receiver system.

BACKGROUND

Modern digital communication requires a sampling receiver to sample ananalog signal, such as a radio frequency (RF) signal and convert thesignal to a digital signal via an analog-to-digital converter (ADC). RFsampling transceivers are implemented in a variety of communicationsarchitectures, such as Wireless Infrastructure (WI), pulse-based RADARsystems, defense systems, and other types of communication systems. In atypical RF sampling transceiver, digital receiver chains typicallyoperate at several phases of a high frequency clock signal (e.g., 3gigabits per second or faster). As a result of the different phases ofthe high frequency clock signal, the digital signal can be provided asmultiple parallel digital streams that are each associated with adifferent phase of the clock signal. Digital clock activity mismatch canresult in clock-coupling spurs in the associated ADC at differentfrequency sub-bands associated with the digital signal. Systems withinterleaved ADC cores can also experience such spurs due to potentialmismatches in DC components added by the different ADC cores. Theclocking spurs can be coupled to the receiver chain inputs and candegrade the resulting input signal. The spurs can also be time varyingin nature, such that the amplitude and phase of the spurs may changeover time.

SUMMARY

One example includes a receiver system. The receiver system includes ananalog-to-digital converter (ADC) configured to convert an analog inputsignal into a digital output signal at a sampling frequency. Thereceiver system also includes a spur correction system configured toreceive the digital output signal and to estimate spurs associated withthe digital output signal and to selectively correct a subset of thespurs associated with a set of frequencies that are based on thesampling frequency.

Another example includes a method for correcting spurs in a sequence ofdigital samples in a receiver system. The method includes converting ananalog input signal into a digital output signal at a sampling frequencyand generating a current spur estimate for each frequency of a set offrequencies associated with the digital output signal. The method alsoincludes generating at least one spur correction estimate for a selectedat least one frequency of the set of frequencies associated with thedigital output signal. The method further includes correcting arespective at least one spur associated with each of the at least onefrequency of the set of frequencies based on the respective at least onespur correction estimate.

Another example includes a receiver system. The receiver system includesan ADC configured to convert an analog input signal into a digitaloutput signal at each of a sequence of samples based on a clock signalhaving a sampling frequency. The system also includes a spur correctionsystem configured to provide a spur correction estimate to correct aspur associated with a given sample of the sequence of samples. The spurcorrection system includes a spur estimator configured to generate acurrent spur estimate at each frequency of the set of frequencies and aspur estimate filter configured to generate the spur correction estimatefor each of at least one of the set of frequencies, the spur estimatefilter being further configured to correct a respective at least onespur associated with the digital output signal based on the respectivespur correction estimate. The spur correction system also includes asignal detector configured to determine whether a signal is presentamong the subset of the set of frequencies. The spur correction systemfurther includes a spur estimate selector configured to save the currentspur estimate as a saved spur estimate when a signal is not detectedamong a block of consecutive samples and to set the spur correctionestimate to the respective current spur estimate in response to thesignal detector not detecting the presence of the signal among thesubset of the set of frequencies, and to set the spur correctionestimate to the saved spur estimate in response to the signal detectordetecting the presence of the signal among the subset of the set offrequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a spur-estimating receiver.

FIG. 2 illustrates an example of a signal detector.

FIG. 3 illustrates an example diagram of signal presence detection.

FIG. 4 illustrates an example of a spur correction system.

FIG. 5 illustrates another example of a signal detector.

FIG. 6 illustrates an example of a spur estimate selector.

FIG. 7 illustrates an example of a method for estimating a sampling spurin a receiver system.

DETAILED DESCRIPTION

This disclosure relates generally to electronic systems, and morespecifically to a spur-estimating receiver system. The receiver systemcan be implemented in any of a variety of digital communication systemsin which analog signals (e.g., communication signals) are received andconverted to digital signals. As described herein, the term “receiver”is used throughout, but it is to be understood that the spur estimatingreceiver system is not limited to use in a receiver system, and that theprinciples described herein are equally applicable to the receiverportion of a transceiver system. The spur-estimating receiver system caninclude an analog-to-digital converter (ADC) that is configured toconvert an analog input signal to a digital output signal at each of asequence of samples based on a clock signal having a sampling frequency.As an example, the sampling frequency can be high frequency (e.g., 3gigabits per second or higher), and the clock signal can have a lowerfrequency (e.g., 375 MHz or 750 MHz), such that the analog signal afterconversion to digital is sent out as multiple parallel digital outputsignal streams at different phases of the lower rate clock signal.

Such a receiver system may be affected by spurs that couple to the inputports that receive the desired signal. These spurs typically have afixed frequency with slow variation in amplitude and phase of the spuracross time. Further, the high-rate ADC (e.g., operating atapproximately 3 giga-samples per second (GSPS)) may be implemented usingmultiple component ADCs operating at a lower rate but at differentphases to create an overall sampled data (e.g., at 3 GSPS). This can berealized, for example, using four component ADCs operating at fourrespective phases (e.g., of a 750 MHz clock) or by two component ADCsoperating at two respective phases (e.g., of a 1.5 GHz clock). In thiscase, the direct current (DC) added by each of the component ADCs may bedifferent thereby causing spurs, such as at 0, fs/4, and fs/2 in theexample of four component ADCs, or spurs at 0 and fs/2 in the example oftwo component ADCs. Therefore, spurs can be located at kfs/N, where k=0,1, . . . N/2, where N is the number of parallel streams or the number ofcomponent interleaved ADCs. The spurs that couple into the receivedsignal can therefore cause undesirable effects in the receiver system.However, it may not be necessary to remove all of spurs at all of therespective kfs/N locations (e.g., for all k values corresponding to anindex of the component ADC) to mitigate undesirable effects. Forexample, due to the nature of the coupling, some spurs may be strongwhile others may be very weak. As another example, some spurs may residein the band of the received signal thereby affecting its reception whilesome spurs may reside outside of the band of the received signal.

The receiver system includes a spur correction system configured toreceive the digital output signal and to provide spur correctionestimates to correct the received spurs. As described herein, the term“spur correction” refers to removing a spur from a sample based onsubtracting a spur correction estimate from a given digital sample thatincludes the spur. The spur correction system can include, for example,four component functions: basic spur estimation, filtering of spurestimates to correct only relevant spurs, signal-power detection thatcan detect if the spur estimates are affected by presence of signal, anda spur estimate selection state machine that can determine the finalcorrection to be applied.

For example, a basic spur estimation module can compute spur estimatesfor all the spurs of interest for every sample. As an example, thereceiver can implement a parallelized digital implementation case, whereeach input signal stream can operate at different phases of the lowerrate clock signal. Therefore, a set of N narrow-band filters generatesestimates, all of which can be aggregated together to result in spurestimates at all kfs/N, k=0 . . . N/2.

A spur estimate filter can operate on the output of the basic spurestimation module and can filter the output such that only spurs ofinterest can be removed. In the case of the parallel implementationwhere the spurs are located at kfs/N, k=0 . . . N/2, the spur estimatefilter can be realized using simple filters. For example, the filter canreceive inputs from other streams and can filter each of the streamswith data from other streams, so that spurs at the sub-bands of interestare passed and other spurs are suppressed. Therefore, the output of thisspur estimate filter module can be used to correct spurs in the inputsignal in the relevant sub-bands of interest.

The spur correction system may additionally employ a signal detectorthat detects if signal is present around the frequency bands ofinterest. If signal presence is detected, then the spur estimateselector (e.g., via an associated state machine) can determine the spurcorrection to be performed. The signal detector may be implemented inmany ways. For example, the spur correction system can include a signaldetector that is configured to implement both narrow-band filtering andwide-band filtering to determine the presence of the signal. The spurcorrection system can also include a signal presence detector that isconfigured to subtract a narrow-band filter output from a wide-bandfilter output for each of the samples to generate a difference. Inresponse to the power of the difference being greater than apredetermined threshold, the signal presence detector can determine thatthere is a signal present in the respective sample. Additionally, thesignal presence detector can compare the narrow-band power level withthe power of the current saved spur estimate, which is obtained when asignal is determined to be not present (or alternately relative to apower threshold), and can determine that there is a signal present ifthe narrow-band power level is greater than the saved spur estimate (orrelative to the power threshold).

Additionally the narrow-band and wide-band filter outputs in the signaldetector may be passed through (e.g., different instances of) spurestimate filters so that the narrow-band and wide-band powers or samplesonly reflect signal content in the sub-bands of interest. The output ofthese modified narrow and wide-band filters may be passed throughprocessing, such as described previously, to detect signal presence.

The spur correction estimate can be equal to a current spur estimateassociated with the respective given sample in response to not detectingthe presence of the signal across the frequency band associated with thegiven sample. Therefore, in response to not detecting a signal acrossthe frequency band in the respective given sample, the spur correctionsystem can correct the given sample based on the estimated spurassociated with the respective given sample itself. The spur correctionestimate can also be set equal to a saved spur estimate corresponding toa spur estimate of a previous sample in which no signal was detected inresponse to the signal detector detecting the presence of the signalacross the frequency band associated with the given sample.

As an example, the spur correction system can include a spur estimatorstate machine that is configured to operate in a first state in responseto greater than or equal to a predetermined threshold of samples of ablock of sequential samples being determined to include no signal and ina second state in response to less than the predetermined threshold ofsamples of the block of sequential samples being determined to includeno signal. In the first state, the spur correction system can set thesaved spur estimate equal to the current spur estimate associated with arespective current sample and can set the spur correction estimate to beequal to the current spur estimate associated with each respective givensample of a next subsequent block of sequential samples. In the secondstate, the spur correction system can set the spur correction estimateto be equal to the saved spur estimate for each respective given sampleof a next subsequent block of sequential samples.

FIG. 1 illustrates an example of a spur-estimating receiver system 100.The spur-estimating receiver system 100 can be implemented in any of avariety of digital communication systems in which analog signals (e.g.,communication signals) are received and converted to digital signals.For example, the spur-estimating receiver system 100 can be implementedin an RF feedback sampling transceiver.

The spur-estimating receiver system 100 includes an analog-to-digitalconverter (ADC) 102 that is configured to convert an analog inputsignal, demonstrated in the example of FIG. 1 as a signal “AN_IN”, to adigital output signal, demonstrated in the example of FIG. 1 as a signal“DIG_OUT”, at each of a sequence of samples based on a clock signal CLKhaving a sampling frequency. As an example, the sampling frequency canbe high frequency (e.g., 3 gigabits per second or higher). Therefore,the analog input signal AN_IN can be sampled at multiple differentphases of the clock signal CLK to provide for multiple parallel digitaloutput signal streams DIG_OUT, as described in greater detail herein.The spur-estimating receiver system 100 can therefore provide spurcorrection for each of the parallel digital output signal streamsDIG_OUT.

The spur-estimating receiver system 100 also includes a spur correctionsystem 104 configured to receive the digital output signal DIG_OUT andto determine whether there is a signal present across a frequency bandassociated with a given sample of the sequence of samples. The spurcorrection system 104 can thus provide a spur correction estimate tocorrect a spur associated with the given sample based on whether thereis a presence of or absence of a signal in the respective sample. Thestream of corrected samples corresponding to the digital output signalDIG_OUT having been spur-corrected by the spur correction system 104 isdemonstrated as being output from the spur correction system 104 as asignal “SMPL”. For example, the stream of corrected samples SMPL can bea spur-corrected serial sample stream after parallelization andre-serialization by the spur correction system 104. In the example ofFIG. 1, the spur correction system 104 includes a spur estimator 106 anda signal detector 108. The spur estimator 106 is configured to generatea current spur estimate for each respective sample of the digital outputsignal DIG_OUT. The current spur estimate thus corresponds to anestimated spur component of the instant respective sample that isevaluated by the spur estimator 106.

The signal detector 108 is configured to evaluate each of the samples inthe digital output signal DIG_OUT to determine if there is a signalpresent around the subset of kfs/N bands of interest. Presence ofsignals around the kfs/N bands may be due to communication signals nearthe respective bands. For example, for fs=3 GHz, if there are signalbands near 3.75 GHz, then the signal bands can alias and fall at 750MHz. The estimates of the spurs of the system at 750 MHz can be affectedby the presence of the signals as the signals may degrade the quality ofthe estimate of the spur at 750 MHz. If uncorrected, the spur at 750 MHzcan affect the reception of the signal band by the receiver and degradeperformance of the receiver. As an example, the signal detector 108 caninclude a set of filters that are configured to provide filtering of afrequency band associated with each respective sample to determine thepresence or absence of the signal in the respective sample. For example,the signal detector 108 can implement both narrow-band filtering andwide-band filtering of each sample of the digital output signal DIG_OUTto determine the presence of the signal. The signal detector 108 canthus subtract a narrow-band filter output sample from a wide-band filteroutput sample to generate a difference. Therefore, the signal detector108 can compare the power of the sample difference with a predeterminedthreshold, such that the signal detector 108 can determine that there isa signal present in the respective sample in response to the power beinggreater than a predetermined threshold. Additionally, the signaldetector 108 can compare the narrow-band power level with the currentspur estimate of the respective sample (or alternately a powerthreshold), and can determine that there is a signal present if thenarrow-band power level is greater than the current spur estimate (orthe power threshold).

In response to not detecting the presence of the signal across thefrequency band associated with the given sample, the spur correctionsystem 104 can set the spur correction estimate equal to the currentspur estimate associated with the respective given sample. Therefore, inresponse to not detecting the signal across the frequency band in therespective given sample, the spur correction system 104 can correct thegiven sample based on the estimated spur associated with the respectivegiven sample itself. In response to detecting the presence of the signalacross the frequency band associated with the given sample, the spurcorrection system 104 can set the spur correction estimate equal to asaved spur estimate corresponding to a spur estimate of a previoussample where the signal presence was not detected. Therefore, inresponse to not detecting the signal across the frequency band in therespective given sample, the spur correction system 104 can correct thegiven sample based on a spur estimate associated with a previous sample.As a result, the spur correction system 104 can correct the spur of thegiven sample that includes a signal while substantially mitigatingdistortion of the resulting signal.

In addition, in the example of FIG. 1, the spur estimator 106 includes afirst spur estimate filter 110. The spur estimate filter 110 canfacilitate selective operation on the output of the spur estimator 106and can filter the output such that only spurs of interest can beremoved. For example, in the case of the parallel implementation wherethe spurs are located at kfs/N, k=0 . . . N/2, the spur estimate filter110 can be realized using simple filters (e.g., finite impulse response(FIR) filters). For example, the spur estimate filter 110 can select asubset of the spur estimates output from parallel filters associatedwith the spur estimator 106 to selectively correct the subset of thespurs associated with the set of frequencies in response to a selectionsignal. For example, for N=8, if spur correction is selected for DC, forfs/4 and for fs/2, then the filter to be used can be expressed as(1+z⁻⁴)/2. Such a filter response can be expressed as unity at DC, fs/4,and for fs/2, and can be expressed as 0 at fs/8 and at 3fs/8, therebyeffectively allowing only estimates at DC, fs/4, and fs/2. As anotherexample, in a simple implementation, the output of this spur estimatefilter 110 can be used to correct spurs in the digital output signalDIG_OUT.

In addition, in the example of FIG. 1, the signal detector 108 includesa second spur estimate filter 111. The spur estimate filter 111 canfacilitate signal detection in only the desired sub-bands and can filterthe narrow-band and wide-band outputs such that only signal bands ofinterest can be observed and power detected only in the desiredsub-bands. For example, in the case of the parallel implementation wherethe spurs are located at kfs/N, k=0 . . . N/2, the spur estimate filter111 can be realized using simple filters (e.g., finite impulse response(FIR) filters). For example, two different instantiations of the spurestimate filter 111 can filter the narrow-band and wide-band signalsseparately. The output of the sub-band filtered narrow-band andwide-band signals are then used for power detection as before, where thedifference in the sub-band filtered narrow-band sample and sub-bandfiltered wide-band sample is implemented as described previously. Forexample, for N=8, if spur correction is selected for DC, for fs/4, andfor fs/2, then the filter to be used can be expressed as (1+z⁻⁴)/2. Sucha filter response can be expressed as unity at DC, fs/4, and for fs/2,and can be expressed as 0 at fs/8 and at 3fs/8. The narrow-band andwide-band filter outputs when sent through two instantiations of thespur estimate filter, result in narrow-band and wide-band signals onlyaround DC, fs/4, and fs/2. Signal detection on the two outputs can bedetermined by looking at the power of the difference between these twooutputs if signals are present near DC, fs/4, or fs/2. As an example, ifsignals are present only near fs/8 or 3fs/8, then the output of both thefilters will be approximately identical, thereby rendering thedifference approximately zero to indicate that no signal presence isdetected. Thus, the signal detector 108 interprets the estimates asvalid since no signal is present near the spurs of interest at DC, fs/4,or fs/2.

As described in greater detail herein, the spur correction system 104can operate as a state machine. For example, the spur correction system104 can operate in a first state in response to greater than or equal toa predetermined threshold of samples of the block of sequential samplesbeing determined to include no signal and in a second state in responseto less than the predetermined threshold of samples of the block ofsequential samples being determined to include no signal. Therefore, inthe first state, the spur correction system 104 can set the saved spurestimate equal to the current spur estimate associated with a respectivecurrent sample and can set the spur correction estimate to be equal tothe current spur estimate associated with each respective given sampleof a next subsequent block of sequential samples. In the second state,the spur correction system 104 can set the spur correction estimate tobe equal to the saved spur estimate for each respective given sample ofa next subsequent block of sequential samples.

FIG. 2 illustrates an example diagram of a signal detector 200. Thesignal detector 200 can correspond to the signal detector 108 in theexample of FIG. 1. Therefore, reference is to be made to the example ofFIG. 1 in the following description of the example of FIG. 2.

The signal detector 200 is demonstrated in the example of FIG. 2 asincluding at least one narrow-band filter 202 and at least one wide-bandfilter 204. The narrow-band filter(s) 202 and wide-band filter(s) 204are each configured to input the digital output signal DIG_OUT.Therefore, each of the narrow-band filter(s) 202 and wide-band filter(s)204 are configured to filter signals to only allow frequency bandsaround kfs/N, of the digital output signal DIG_OUT to determine thepresence or absence of the signal around kfs/N bands in the respectivesample. The narrow-band filter(s) 202 are configured to generate anarrow-band portion, demonstrated in the example of FIG. 2 as a signal“PN”, corresponding to a filtered portion of the sample associated withnarrow frequency-bands centered around kfs/N frequencies of therespective sample of the digital output signal DIG_OUT. Similarly, thewide-band filter(s) 204 are configured to generate a wide-band portion,demonstrated in the example of FIG. 2 as a signal “PW”, corresponding toa filtered portion associated with moderately wide (e.g., wider than thenarrow-band selected by the narrow-band filter) frequency-bands centeredaround kfs/N frequencies of the respective sample of the digital outputsignal DIG_OUT, with the frequency band being greater in width than thenarrow-band associated with the narrow-band filter(s) 202. As anexample, the narrow-band filter(s) 202 and the wide-band filter(s) 204can be configured as any of a variety of types of filters, such asfirst-order infinite impulse response (IIR) filters operating onindividual data streams with each operating at fs/N sampling rate. Forexample, an IIR filter of the form αz^(−N)/(1−(1−α)z^(−N)) with verysmall a operates as a filter having pass bands around kfs/N. The α areselected to be very small for the narrow-band filter and larger (butstill relatively small in absolute terms) for the wide-band filters. Thefilters, when implemented on individual streams each operating at fs/N,can operate at αz⁻¹/(1−(1−α)z⁻¹), and thus as a simple first order IIRfilter.

In the example of FIG. 2, the narrow-band portion PN and the wide-bandportion PW are provided to a signal presence detector 206. The signalpresence detector 206 can be configured to determine the presence orabsence of a signal in the respective sample based on the narrow-bandportion PN relative to the wide-band portion PW. For example, the signalpresence detector 206 can be configured to sample the narrow-bandportion PN and the wide-band portion PW, and can subtract thenarrow-band portion PN sample from the wide-band portion PW sample togenerate a difference sample. The signal presence detector 206 can thuscompare the power of the difference sample with a predeterminedthreshold, demonstrated in the example of FIG. 2 as a signal “THRSH”. Inresponse to the power of the difference sample being greater than orequal to the predetermined threshold THRSH, the signal presence detector206 can determine that there is a signal present in the respectivesample. Alternatively, in response to the power of the difference samplebeing less than the predetermined threshold THRSH, the signal presencedetector 206 can determine that there is no signal present in therespective sample.

FIG. 3 illustrates an example diagram 300 of signal presence detection.The diagram 300 demonstrates four different stages of processing forsignal presence detection of the digital output signal DIG_OUT, that isassociated with a frequency band that is centered at a frequencyk*F_(S)/N that is associated with a frequency F_(S) of the clock signalCLK. For example, “N” can correspond to a quantity of parallel samplingstreams of the digital output signal DIG_OUT (e.g., associated withinterleaved ADCs). Therefore, in the example of FIG. 3, the frequencyband is defined as a frequency band centered at approximately thefrequency k*F_(S)/N from approximately a frequency −F to approximately afrequency +F. While the frequency band in the example of FIG. 3 isdemonstrated as being approximately symmetric about the frequencyk*F_(S)/N, it is to be understood that the frequency band can benon-uniform about the frequency k*F_(S)/N.

The diagram 300 demonstrates a first stage 302 that demonstrates thefrequency spectrum 304 of the digital output signal DIG_OUT, definedbetween the frequency −F and the frequency +F centered at the frequencyk*F_(S)/N. The frequency spectrum includes a spur component “SPR” thatis located at the frequency k*F_(S)/N. For example, the spur componentSPR can have resulted from digital clock activity mismatch in the ADC102 at different frequency sub-bands based on the N parallel samplingstreams.

The diagram 300 also includes a second stage 306 that demonstrates thesample that is wide-band filtered by a respective wide-band filter 204.In the second stage 306, the sample is demonstrated as removing portionsof the frequency spectrum 304 between the frequency −F and the frequency+F. The frequency spectrum includes the spur component “SPR” that islocated at the frequency k*F_(S)/N. In the example of FIG. 3, therespective wide-band filter 204 passes a portion of the frequencyspectrum 304 between a frequency −WB and a frequency +WB to provide awide-band portion 308, with the wide-band portion 308 being centeredabout the frequency k*F_(S)/N. Therefore, the original bandwidth of thefrequency spectrum 304 is demonstrated in the example of FIG. 3 as beingoutlined with a dotted line. The wide-band portion 308 in the secondstage 306 can thus correspond to an output of the wide-band filter 204between the frequency −WB and the frequency +WB corresponding to awide-band power level.

The diagram 300 also includes a third stage 310 that demonstrates thesample that is narrow-band filtered by a respective narrow-band filter202. In the third stage 310, the sample is demonstrated as removingportions of the frequency spectrum 304 between the frequency −F and thefrequency +F. The frequency spectrum includes the spur component “SPR”that is located at the frequency k*F_(S)/N. In the example of FIG. 3,the respective narrow-band filter 202 passes a portion of the frequencyspectrum 304 between a frequency −NB and a frequency +NB to provide anarrow-band portion 312, with the narrow-band portion 312 being centeredabout the frequency k*F_(S)/N. The narrow-band portion 312 therefore hasa narrower frequency band than the wide-band portion 308. The originalbandwidth of the frequency spectrum 304 is demonstrated in the exampleof FIG. 3 as being outlined with a dotted line. The narrow-band portion312 in the third stage 310 can thus correspond to an output of thenarrow-band filter 202 between the frequency −NB and the frequency +NB.

The diagram 300 further includes a fourth stage 314 that demonstratesthe sample corresponding to the narrow-band portion 312 subtracted fromthe sample corresponding to the wide-band portion 308. As describedpreviously, the signal presence detector 206 is configured to subtractthe narrow-band sample from the wide-band sample to obtain a difference.In the example of FIG. 3, the fourth stage 314 demonstrates the spectrumof the difference between the sample corresponding to the narrow-bandportion 312 and the sample corresponding to the wide-band portion 308corresponding to a difference sample 316. The difference sample 316 isdemonstrated as including a first difference band −ΔF and a seconddifference band +ΔF that is approximately centered at the frequencyk*F_(S)/N. As described previously, the signal presence detector 206 cancompare a power of the difference sample 316 with the predeterminedthreshold THRSH. In response to the power of the difference sample 316being greater than or equal to the predetermined threshold THRSH, thesignal presence detector 206 can determine that there is a signalpresent in the respective digital output signal DIG_OUT around kfs/N.Alternatively, in response to the difference power level being less thanthe predetermined threshold THRSH, the signal presence detector 206 candetermine that there is no signal present in the respective digitaloutput signal DIG_OUT around kfs/N.

Referring back to the example of FIG. 2, the signal presence detector206 receives a signal SE. As an example, the signal SE can correspond tothe saved spur estimate that was determined to have no signal present orthat which is not corrupted by the presence of the signal. The signalpresence detector 206 can thus also compare the power of the narrow-bandsample with the current spur estimate SE. As an example, a suddennarrow-band input signal can degrade the narrow-band sample output (thenarrow-band sample output has the spur at fs/N+any signal present in anarrow-band around fs/N). If the power difference between the power ofthe narrow-band sample and the current spur estimate SE is high (e.g.,greater than a second predetermined threshold), then the signal presencedetector 206 can determine that a sudden narrow-band input signal ispresent given that the saved spur estimate SE typically does not changemuch over time (e.g., typically approximately −65 dBFs fromsample-to-sample). Therefore, in response to determining that thedifference between the power of the narrow-band sample and the currentspur estimate SE is sufficiently high (e.g., greater than the secondpredetermined threshold), then the signal presence detector 206 candetermine that there is a signal present in the respective digitaloutput signal DIG_OUT. In this way, the signal presence detector 206 canprovide an additional robustness to the determination of the presence ofthe signal in the respective sample given that an initial saved spurestimate is obtained when there is no actual signal present input (e.g.,during power-up or calibration), and so is therefore accurate, and thatfurther changes to the saved spur estimate occurs typically in theabsence of a wide-band or narrow-band signal. As an example, the savedspur estimate can be equal to the estimate during initial or power-upcalibration when there is no input, and hence serves as a reasonablereference. Also, instead of comparing the power of the narrow-bandfilter output sample with the saved power of the spur estimate, thepower of the difference between narrow-band filter output and the savedspur estimate can be computed.

In response to the determination of no signal being present in therespective sample, the signal presence detector 206 can be configured toprovide a first state of a validation signal, demonstrated in theexample of FIG. 2 as a signal “VB”. For example, the signal presencedetector 206 can assert the validation signal VB to indicate that therespective sample does not include a signal, and therefore is a validsample for correcting the spur using the current spur estimate.Additionally, in response to the determination of a signal being presentin the respective sample, the signal presence detector 206 can beconfigured to provide a second state of the validation signal VB.Therefore, as an example, the signal presence detector 206 can de-assertthe validation signal VB to indicate that the respective sample includesa signal, and therefore is not a valid sample for correcting the spurusing the current spur estimate. As a result, the spur correction system104 can correct the spur of the respective sample based on the savedspur estimate.

FIG. 4 illustrates an example of a spur correction system 400. The spurcorrection system 400 can correspond to the spur correction system 14 inthe example of FIG. 1. Therefore, reference is to be made to theexamples of FIGS. 1-3 in the following description of the example ofFIG. 4.

As described previously, the spur correction system 400 is configured toreceive the digital output signal DIG_OUT and to determine whether thereis a signal present across a frequency band associated with a givensample of the sequence of samples. The spur correction system 400 canthus provide a spur correction estimate to correct a spur associatedwith the given sample based on whether there is a presence of or absenceof a signal in the respective sample. In the example of FIG. 4, thestream of corrected samples corresponding to the digital output signalDIG_OUT having been spur-corrected by the spur correction system 400 isdemonstrated as being output from the spur correction system 400 as asignal “SMPL”.

In the example of FIG. 4, the spur correction system 400 includes a spurestimator 402. The spur estimator 402 is configured to parallelize thedigital output signal DIG_OUT, demonstrated in the example of FIG. 4 as“N” parallel digital output signal streams, similar to as describedpreviously in the example of FIG. 3. The spur estimator 402 is furtherconfigured to generate a current spur estimate for each respectivesample of each of the parallel digital output signal streams. Forexample, the spur estimator 402 can include a parallel set of filters(e.g., IIR filters) that are each associated with a separate phase ofthe sampling frequency of the clock signal CLK. The output of the spurestimator 402 in all the parallel chains effectively obtains the spursat all kfs/N (k=0, 1, . . . N/2) frequency locations based on theindividual low pass filters in each of the parallel chains, takentogether, producing the estimates at all kfs/N collectively. Thiscurrent spur estimate (the sequence of N values) thus corresponds to anestimated spur component of the current respective sample.

The spur correction system 400 also includes a signal detector 404configured to evaluate each of the samples in each of the paralleldigital output signal streams to determine if there is a signal presentin the digital output signal DIG_OUT. Similar to as describedpreviously, the signal detector 404 can include a set of filters thatare configured to provide filtering of multiple frequency bandsassociated with the parallel digital signal streams to determine thepresence or absence of the signal. For example, the signal detector 404can implement both narrow-band filtering and wide-band filtering of eachsample of each of the parallel digital output signal streams todetermine the presence of the signal. The signal detector 404 can thussubtract a narrow-band sample from a wide-band sample with respect toeach filtered sample to generate a set of N difference samples.Therefore, the signal detector 404 can compare the power of the set ofdifference samples with a predetermined threshold, such that the signaldetector 404 can determine that there is a signal present in therespective sample in response to the power of the difference samplebeing greater than a predetermined threshold.

FIG. 5 illustrates an example diagram of a signal detector 500. Thesignal detector 500 can correspond to the signal detector 404 in theexample of FIG. 4. Therefore, reference is to be made to the example ofFIG. 4 in the following description of the example of FIG. 5.

The signal detector 500 includes a serial-to-parallel converter 502 thatis configured to convert the digital output signal DIG_OUT into the Nparallel digital output signal streams, demonstrated in the example ofFIG. 5 as signals DIG₁ through DIG_(N). Therefore, each of the digitaloutput signal streams DIG₁ through DIG_(N) can correspond to a separatephase associated with the clock signal CLK. The signal detector 500 alsoincludes a narrow-band filter and wide-band filter pair for each of therespective digital output signal streams DIG₁ through DIG_(N),demonstrated in the example of FIG. 5 as narrow-band filters 504 andwide-band filters 506. Therefore, each sample of each of the digitalsignal streams DIG₁ through DIG_(N) is filtered by each of a narrow-bandfilter 504 and a wide-band filter 506. The narrow-band filters 504 areeach configured to generate a respective narrow-band portion PN₁ throughPN_(N), similar to the narrow-band portion 312 in the example of FIG. 3,and the wide-band filters 506 are each configured to generate arespective wide-band portion PW₁ through PW_(N), similar to thewide-band portion 308 in the example of FIG. 3. For example, thenarrow-band filters 504 and the wide-band filters 506 can each beconfigured as first order IIR filters.

The narrow-band portions PN₁ through PN_(N) and the wide-band portionsPW₁ through PW_(N), in aggregate, correspond to a narrow-band andwide-band signal around all kfs/N, k=0, 1, . . . N/2. Therefore, inorder to separate the narrow-band portions PN₁ through PN_(N) and thewide-band portions PW₁ through PW_(N), the narrow-band portions PN₁through PN_(N) and the wide-band portions PW₁ through PW_(N) are eachprovided to a parallel-to-serial converter 508. The parallel-to-serialconverter 508 is configured to provide a first serial stream of thenarrow-band portions PN₁ through PN_(N), demonstrated as a signal NB,and a second serial stream of the wide-band portions PW₁ through PW_(N),demonstrated as a signal WB. The signals NB and WB thus each correspondto signals that are low-pass filtered around all k*F_(S)/N samples.

In the example of FIG. 5, the signals NB and WB are provided to a spurestimate filter 510. The spur estimate filter 510 includes a sub-bandfilter 512. The sub-band filter 512 can be configured to filter outundesired sub-bands associated with the signals NB and WB to provide forspecific sub-bands for determination of a signal. For example, thesub-band filter 512 in the spur estimate filter 510 can each include oneor more finite impulse response (FIR) filters. As a result, the sub-bandfilter 512 can remove the undesired sub-bands from the respectivesignals NB and WB and pass the remaining respective portions,demonstrated in the example of FIG. 5 as signals SBN and SBW,respectively.

The outputs SBN and SBW of the sub-band filter 512 are provided to aserial-to-parallel converter 514, and the serialized outputs are sampledvia respective samplers 516 and 518 to each provide N samples,demonstrated as S_(N) and S_(W), respectively, to a signal presencedetector 520. Therefore, each corresponding pair of the sub-bands SBNand SBW can be associated with a given respective one of the N samples.The signal presence detector 520 can be configured to determine thepresence or absence of a signal. For example, the signal presencedetector 520 can operate substantially similarly to the signal presencedetector 206 described previously in the example of FIG. 2. For example,the signal presence detector 520 can subtract the narrow-band sampleassociated with a respective one of the sub-bands SBN from the wide-bandsample associated with a respective one of the sub-bands SBW to generatea respective difference sample. The signal presence detector 520 canthus compare the sum of powers of the difference samples with apredetermined threshold (e.g., the signal “THRSH” in the example of FIG.2). In response to the sum of power of the difference samples beinggreater than or equal to the predetermined threshold, the signalpresence detector 520 can determine that there is a signal present inthe respective sub-band. However, in response to the sum of power of thedifference samples being less than the predetermined threshold, thesignal presence detector 520 can determine that there is no signalpresent in the respective sub-band.

Additionally, similar to as described previously regarding the exampleof FIG. 2, the signal presence detector 520 can detect narrow-bandsignals in the respective sub-band. In the example of FIG. 5, the signalpresence detector 520 receives the signals SBN and SBW corresponding tosub-band filtered outputs sampled from the outputs of the sub-bandfilter 512. As an example, the signals SBSE₁ through SBSE_(N) cancorrespond to the respective sub-band filtered saved spur estimates andthe signals InitSE₁ through InitSE_(N) can correspond to the sub-bandfiltered initial spur estimates that are obtained during some power upor initial calibration, where it is known that signals are absent andhence can be taken as reliable estimates of spur level at that time. AMx_Sel signal control a multiplexer (MUX) 522 that selects between thetwo sets of signals SBSE₁ through SBSE_(N) and InitSE₁ throughInitSE_(N) and provides the selected signals as signals SelSE₁ toSelSE_(N) to the signal presence detector 520. The signal presencedetector 520 can thus also compare the power of the narrow-band sampleassociated with the corresponding sub-band SBN with the respective oneof the spur estimates SelSE₁ through SelSE_(N). If the sum of the powerdifference between the respective narrow-band sample (e.g., SBN₁ throughSBN_(N)) and the respective mux-selected spur estimate SelSE₁ throughSelSE_(N) is greater than a second predetermined threshold, then thesignal presence detector 520 can determine that there is a signalpresent in the respective sample. However, if the power differencebetween the respective narrow-band sample SBN₁ through SBN_(N) andrespective mux-selected saved spur estimate SelSE₁ through SelSE_(N) isless than the second predetermined threshold, then the signal presencedetector 520 can determine that there is no signal present.

In response to the determination of no signal being present, the signalpresence detector 520 can be configured to provide a first state of avalidation signal, demonstrated in the example of FIG. 5 as a signal VB.For example, the signal presence detector 520 can assert the validationsignal VB to indicate that the respective corresponding set of samplesdoes not include a signal. Additionally, in response to thedetermination of a signal being present in the respective correspondingset of samples, the signal presence detector 520 can be configured toprovide a second state of a validation signal VB to indicate that therespective set of samples includes a signal.

Referring back to the example of FIG. 4, the spur correction system 400also includes a spur estimate selector 406. The spur estimate selector406 is configured to select between the current spur estimates SE₁through SE_(N) or the saved spur estimates SBSE₁ through SBSE_(N) foreach of the samples associated with the respective digital output signalstreams DIG₁ through DIG_(N). In the example of FIG. 4, the spurestimate selector 406 receives the current spur estimates SE₁ throughSE_(N) from the spur estimator 402 and receives the validation signal VBform the signal detector 404 corresponding to the samples DIG_OUT₁through DIG_OUT_(N). Therefore, as an example, in response todetermining that a given set of N samples is valid based on thevalidation signal VB, and therefore does not include a signal, the spurestimate selector 406 can be configured to use the respective currentspur estimate SE₁ through SE_(N) to correct the spur of the sampleassociated with the respective one of the digital output signal streamsDIG₁ through DIG_(N). Similarly, in response to determining that a givenset of N samples is not valid based on the validation signal VB, andtherefore includes a signal, the spur estimate selector 406 can beconfigured to use the respective saved spur estimate (e.g.,corresponding to a respective last valid current spur estimate SBSE₁through SBSE_(N)) to correct the spur of the sample associated with therespective one of the digital output signal streams DIG₁ throughDIG_(N).

As another example, the spur estimate selector 406 can include statemachines that can be implemented for the evaluation of and correction ofa block of sequential samples of the respective digital output signalstreams DIG₁ through DIG_(N). For example, the respective state machinescan be configured to count a quantity of samples in a given block ofsequential samples of the respective digital output signal streams DIG₁through DIG_(N) that are considered valid based on the validation signalVB. In response to the quantity of samples being equal to or greaterthan a predetermined threshold of valid samples, the respective spurestimator state machine can determine that the next block of sequentialsamples of the respective digital output signal streams DIG₁ throughDIG_(N) should be corrected based on the respective one of the currentspur estimates SE₁ through SE_(N). However, if the quantity of samplesis less than the predetermined threshold of valid samples, therespective spur estimator state machine can determine that the nextblock of sequential samples of the respective digital output signalstreams DIG₁ through DIG_(N) should be corrected based on the saved spurestimate, as described in greater detail herein. The spur estimateselector 406 can thus provide spur correction estimates SC₁ throughSC_(N) that each correspond to either the respective current spurestimate SBSE₁ through SBSE_(N) or a corresponding saved spur estimate.

FIG. 6 illustrates an example of a spur estimate selector 600. The spurestimate selector 600 can correspond to the spur estimate selector 406in the example of FIG. 4. Therefore, reference is to be made to theexamples of FIGS. 4 and 5 in the following example of FIG. 6.

The spur estimate selector 600 is configured to receive each of thecurrent spur estimates SE₁ through SE_(N) from the spur estimator 402.In the example of FIG. 6, the spur estimator state machines 602 isconfigured to store a saved spur estimate 606 in a memory. For example,the spur estimator state machine 602 can be configured as hardware,software, firmware, or a combination thereof. As an example, theselector 604 can be configured as a multiplexer configured to selectbetween two separate spur estimates, as described in greater detailherein.

The spur estimator state machine 602 is configured to evaluate thevalidation signal VB. As an example, each block of sequential samplescan have a predetermined quantity of sequential samples, such that thespur estimator state machine 602 can be configured to count a quantityof the samples in the respective block of sequential samples that areconsidered a valid sample. If the quantity of valid samples is greaterthan the predetermined threshold, then the current spur estimate SE₁through SE_(N) is deemed to be unaffected by signals and so the spurestimator state machine 602 can save the respective current spurestimate SE₁ through SE_(N) (e.g., corresponding to a last sample of theblock of sequential samples) as the saved spur estimate 606. The savedspur estimate 606 is also provided from the spur estimator state machine602 as a signal SBSE₁ through SBSE_(N). The spur estimator state machine602 can also provide a respective selection signal SL₁ through SL_(N)that can be provided to the respective one of the selectors 604 toprovide selection of the spur correction estimate. In the example ofFIG. 6, each of the selectors 604 receives both the respective currentspur estimate SE₁ through SE_(N) and the respective saved spur estimateSBSE₁ through SBSE_(N). Therefore, the respective selection signal SL₁through SL_(N) can determine which of the respective current spurestimate SE₁ through SE_(N) and the respective saved spur estimate SBSE₁through SBSE_(N) is provided as the respective spur correction estimateSC₁ through SC_(N) output from the respective selector 604.

Therefore, in response to the quantity of valid samples being less thanthe predetermined threshold, the spur estimator state machine 602 canprovide the respective selector signal SL₁ through SL_(N) at a firststate. As a result, the selector 604 can provide the respective savedspur estimate SBSE₁ through SBSE_(N) as the respective spur correctionestimate SC₁ through SC_(N). As an example, the respective selectionsignal SL₁ through SL_(N) can be provided in the first state through theentirety of the next block of sequential samples, such that each sampleof the next block of sequential samples can be corrected based on thesaved spur estimate 606. As described previously, the respective savedspur estimate can have been saved based on the last valid set ofrespective current spur estimates SE₁ through SE_(N). Therefore, thesaved spur estimate 606, and thus the respective saved spur estimateSBSE₁ through SBSE_(N), can have a static value throughout the entiretyof the next block of sequential samples for correcting the spur of eachsample of the respective block of sequential digital samples.

Conversely, in response to the quantity of valid samples greater than orequal to the predetermined threshold, the spur estimator state machine602 can provide the respective selector signal SL1 through SLN at asecond state. As a result, the selector 604 can provide the current spurestimate SE₁ through SE_(N) as the respective spur correction estimateSC₁ through SC_(N). As an example, the respective selection signal SL₁through SL_(N) can be provided in the second state through the entiretyof the next block of sequential samples, such that each sample of thenext block of sequential samples can be corrected based on therespective current spur estimate SE₁ through SE_(N). Therefore, therespective current spur estimate SE₁ through SE_(N) of each respectivesample can be provided to correct the spur of the respective sample forwhich the respective current spur estimate SE₁ through SE_(N) wasgenerated by the spur estimator 402 throughout the entirety of the nextblock of sequential samples for correcting the spur of each sample ofthe respective block of sequential digital samples.

Referring back to the example of FIG. 4, the spur correction estimatesSC₁ through SC_(N) are provided to a combiner 408 that is configured toserialize the spur correction estimates SC₁ through SC_(N). Theserialized spur correction estimates are output from the combiner 408 asa signal DIG_C. The serialized spur correction estimates DIG_C areprovided, along with the digital output signal DIG_OUT, to a summationcomponent 410. The summation component 410 is therefore configured tocorrect the spur from the digital output signal DIG_OUT. For example,the summation component 410 is configured to subtract the serializedspur correction estimates DIG_C from the digital output signal DIG_OUTat the appropriate phases of the digital output signal DIG_OUT toprovide spur correction to each sample of the digital output signalDIG_OUT. Accordingly, the summation component 410 outputs a digitalstream SMPL that corresponds to the digital output signal DIG_OUT havingspur corrections.

Based on the operation of the spur correction system 400, as describedherein, to detect the presence or absence of the signal in therespective sample, and to correct the spur of the respective samplebased on the current spur estimate or a saved spur estimate, the spurcorrection system 400 can provide a significantly more accurate andefficient spur correction of the output of the ADC 102 in thespur-estimating receiver system 100. For example, typical spurcorrection systems can implement a notch filter to filter spur from thesample about the notch frequency approximately centered about thefrequency band of the respective sample. However, the typical notchfilter spur correction methods can distort the signal in the respectivesample. Therefore, the spur correction system 400 described herein ismore robust to the presence of high spurs and input signals than typicalnotch filter spur correction methods. Accordingly, as opposed to thetypical spur correction systems, the spur correction system 400described herein can accurately determine the actual spur level andcorrect the spur from the respective samples.

In view of the foregoing structural and functional features describedabove, a methodology in accordance with various aspects of thedisclosure will be better appreciated with reference to FIG. 7. FIG. 7illustrates an example of a method 700 for correcting spurs in asequence of digital samples in a receiver system. It is to be understoodand appreciated that the method of FIG. 7 is not limited by theillustrated order, as some aspects could, in accordance with the presentdisclosure, occur in different orders and/or concurrently with otheraspects from that shown and described herein. Moreover, not allillustrated features may be required to implement a methodology inaccordance with an aspect of the present examples.

At 702, an analog input signal (e.g., the analog input signal AN_IN) isconverted into a digital output signal (e.g., the digital output signalDIG_OUT) at a sampling frequency. At 704, a current spur estimate isgenerated for each frequency of a set of frequencies associated with thedigital output signal. At 706, at least one spur correction estimate isgenerated for the respective selected at least one frequency of the setof frequencies associated with the digital output signal. At 708, arespective at least one spur associated with each of the selected atleast one frequency of the set of frequencies is corrected based on therespective at least one spur correction estimate.

What have been described above are examples of the present invention. Itis, of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the presentinvention, but one of ordinary skill in the art will recognize that manyfurther combinations and permutations of the present invention arepossible. Accordingly, the present invention is intended to embrace allsuch alterations, modifications and variations that fall within thespirit and scope of the appended claims. Additionally, where thedisclosure or claims recite “a,” “an,” “a first,” or “another” element,or the equivalent thereof, it should be interpreted to include one ormore than one such element, neither requiring nor excluding two or moresuch elements. As used herein, the term “includes” means includes butnot limited to, and the term “including” means including but not limitedto. The term “based on” means based at least in part on.

What is claimed is:
 1. A receiver system comprising: ananalog-to-digital converter (ADC) configured to convert an analog inputsignal into a digital output signal at a sampling frequency; and a spurcorrection system configured to receive the digital output signal and toestimate spurs associated with the digital output signal and toselectively correct a subset of the spurs associated with a set offrequencies that are based on the sampling frequency.
 2. The system ofclaim 1, wherein the set of frequencies comprises k*fs/N, “k”corresponds to an index of a respective one of the N interleaved ADCs(k=0, . . . , N/2), and “fs” corresponds to the sampling frequency. 3.The system of claim 2, wherein the spur correction system comprises: aspur estimator configured to generate a current spur estimate at eachfrequency of the set of frequencies; a signal detector configured todetermine whether a signal is present among the selected subset of theset of frequencies; and a spur estimate selector configured to save thecurrent spur estimate as a saved spur estimate when a signal is notdetected among a block of consecutive samples and to set the spurcorrection estimate to the respective current spur estimate in responseto the signal detector not detecting the presence of the signal among asubset of the set of frequencies, and to set the spur correctionestimate to the saved spur estimate in response to the signal detectordetecting the presence of the signal among a subset of the set offrequencies.
 4. The system of claim 2, wherein the spur correctionsystem comprises: a spur estimator configured to generate a current spurestimate at each frequency of the set of frequencies; and a spurestimate filter configured to generate the spur correction estimate foreach of a selected at least one of the set of frequencies, the spurestimate filter being further configured to correct a respective atleast one spur associated with the digital output signal based on therespective spur correction estimate.
 5. The system of claim 4, whereinthe spur estimator comprises a parallel set of filters that are eachassociated with a separate phase of the sampling frequency of a clocksignal corresponding to the set of frequencies to provide the currentspur estimate associated with the respective frequency of the set offrequencies.
 6. The system of claim 5, wherein the spur estimate filteris configured to selectively correct the subset of the spurs associatedwith the set of frequencies.
 7. The system of claim 4, wherein the spurcorrection system further comprises: a signal detector configured todetermine whether a signal is present among the selected subset of theset of frequencies; and a spur estimate selector configured to save thecurrent spur estimate as a saved spur estimate when a signal is notdetected among a block of consecutive samples and to set the spurcorrection estimate to the respective current spur estimate in responseto the signal detector not detecting the presence of the signal among asubset of the set of frequencies, and to set the spur correctionestimate to the saved spur estimate in response to the signal detectordetecting the presence of the signal among a subset of the set offrequencies.
 8. The system of claim 7, wherein the signal detectorcomprises: a narrow-band filter configured to filter the frequency bandassociated with the input signal to generate a narrow-band signal aroundthe set of frequencies; a wide-band filter configured to filter thefrequency band associated with the input signal to generate a wide-bandsignal around the set of frequencies; and a signal presence detectorconfigured to determine the presence or absence of the signal in thefrequency band based on the wide-band filter output and the narrow-bandfilter output.
 9. The system of claim 8, wherein the signal presencedetector is configured to determine a power of a difference between thenarrow-band samples and the wide-band samples to determine the presenceof the signal in the frequency band associated with the given samplebased on the power relative to a predetermined threshold.
 10. The systemof claim 8, wherein the signal detector comprises: a serial-to-parallelconverter configured to convert the digital output signal into aplurality of parallel digital output signals corresponding to arespective plurality of separate phases of the sampling frequency of aclock signal, wherein the narrow-band filter comprises a plurality ofnarrow-band filters and the wide-band filter comprises a plurality ofwide-band filters, such that the signal presence detector is configuredto determine the presence or absence of the signal in the frequencyband.
 11. The system of claim 10, wherein the signal detector furthercomprises: a parallel-to-serial converter configured to convert aplurality of narrow-band filter output samples and a plurality ofwide-band filter output samples corresponding to the respectiveplurality of pairs of narrow-band filters and wide-band filters to aserial set of the plurality of narrow-band filter output samples and theplurality of wide-band filter output samples associated with a sub-bandof the frequency band; a sub-band filter processing the serial set ofnarrow-band samples and a serial set of wide-band samples to generatesub-band filtered narrow-band and wide-band samples, respectively, topass signals in sub-bands of interest and to remove spur estimates inundesired sub-bands.
 12. A method for correcting spurs in a sequence ofdigital samples in a receiver system, the method comprising: convertingan analog input signal into a digital output signal at a samplingfrequency; generating a current spur estimate for a set of frequenciesassociated with the digital output signal; generating at least one spurcorrection estimate for at least one frequency of the set of frequenciesassociated with the digital output signal; and correcting a respectiveat least one spur associated with each of the at least one frequency ofthe set of frequencies based on the respective at least one spurcorrection estimates; wherein generating the current spur estimatecomprises generating the current spur estimate based on a plurality ofparallel filters that are each associated with a separate phase of thesampling frequency associated with a clock signal corresponding to theset of frequencies.
 13. The method of claim 12, further comprising:determining whether a signal is present among the selected subset of theset of frequencies; saving the spur correction estimates in a memory andsetting the spur correction estimate to the current spur estimate inresponse to a determination that the signal is not present in aconsecutive block of samples; and setting the spur correction estimateto the saved spur estimate in response to a determination that thesignal is present in the subset of the set of frequencies.
 14. Themethod of claim 13, wherein determining whether the signal is presentcomprises: filtering the frequency band associated with the input signalvia a narrow-band filter to generate a narrow-band signal around the setof frequencies; filtering the frequency band associated with the inputsignal via a wide-band filter to generate a wide-band signal around theset of frequencies; and determining the presence or absence of thesignal in the frequency band based on the wide-band filter and thenarrow-band filter outputs; determining the presence of absence of thesignal in the frequency band based on a power of the narrow-band signalbeing greater than a scaled value of the power of the saved spurestimate or an initial spur estimate.
 15. The method of claim 14,further comprising converting the digital output signal into a pluralityof parallel digital output signals corresponding to a respectiveplurality of separate phases of the sampling frequency of a clocksignal, wherein the narrow-band filter comprises a plurality ofnarrow-band filters and the wide-band filter comprises a plurality ofwide-band filters, wherein a respective plurality of pairs of thenarrow-band filters and the wide-band filters each correspond to arespective one of the plurality of parallel digital output signals. 16.A receiver system comprising: an analog-to-digital converter (ADC)configured to convert an analog input signal into a digital outputsignal at each of a sequence of samples based on a clock signal having asampling frequency; and a spur correction system configured to provide aspur correction estimate to correct a spur associated with a givensample of the sequence of samples, the spur correction systemcomprising: a spur estimator configured to generate a current spurestimate at each frequency of the set of frequencies; a spur estimatefilter configured to generate the spur correction estimate for each ofat least one of the set of frequencies, the spur estimate filter beingfurther configured to correct a respective at least one spur associatedwith the digital output signal based on the respective spur correctionestimate; a signal detector configured to determine whether a signal ispresent among the subset of the set of frequencies; and a spur estimateselector configured to save the current spur estimate as a saved spurestimate when a signal is not detected among a block of consecutivesamples and to set the spur correction estimate to the respectivecurrent spur estimate in response to the signal detector not detectingthe presence of the signal among the subset of the set of frequencies,and to set the spur correction estimate to the saved spur estimate inresponse to the signal detector detecting the presence of the signalamong the subset of the set of frequencies.
 17. The system of claim 16,wherein the spur estimator comprises a parallel set of filters that areeach associated with a separate phase of the sampling frequency of aclock signal.
 18. The system of claim 16, wherein the signal detectorcomprises: a narrow-band filter configured to filter the frequency bandassociated with the input signal to generate a narrow-band signal aroundthe set of frequencies; a wide-band filter configured to filter thefrequency band associated with the input signal to generate a wide-bandsignal around the set of frequencies; and a signal presence detectorconfigured to determine the presence or absence of the signal in thefrequency band based on the wide-band filter output relative to thenarrow-band filter output.
 19. The system of claim 18, wherein thesignal presence detector is configured to determine a power of adifference between the narrow-band filter output samples and thewide-band filter output samples to determine the presence of the signalin the frequency band associated with the given sample if the differencepower is greater than a predetermined threshold or based on thenarrow-band sample power being greater than a scaled value of the powerof the saved spur estimate or an initial spur estimate.